MULE1.2 Axial flux test motor/bicycle specific
- Thread starter Thud
- Start date
John in CR
100 TW
What is the plan to hold the cores in place, since they aren't part of a strong metal structure used in a radial flux motor? If each core is separate then the flat wind ribbon copper seems like a requirement to avoid the cores and windings becoming loose. What will then hold the windings plus core in place thru the repeating pushing and pulling during high power operation that LFP wants?
rhitee05
10 kW
Thud said:
I agree with Miles, I think it would be worth your while to try and put teeth on the cores. I you look at the models I posted several pages ago, I modeled one case with just plugs and another with plugs+teeth. The teeth help to "gather" the flux into the cores more than just the plugs alone.
The ideas several folks have posted for the laminations running crosswise look nice. That would be the optimal orientation for lams. Laminated construction seems like it would be tricky and time-consuming. Molding cores out of powdered material would probably be easier. Not sure about relative performance between the two methods.
rhitee05
10 kW
I just realized that I fail at math. Those 22.5 deg wedge mags are 1/16 of a circle, not 1/8 as I posted before. The 14-magnet rotors look nice. I can't quite see what the spacing is on your drawing - 1/4"? It would be nice if you could keep the airgap smaller than that, to help reduce flux leaking from one magnet to the next without passing through the stator. If you could get an 1/8" airgap I'd say that's golden.
liveforphysics
100 TW
rhitee05 said:
An airgap of only half the magnet thickness? Is this a trade-off of lessened/deformed flux off each magnet in exchange for tighter stator flux containment? Is there some way to find the optimization for this?
Thud
1 MW
Air gap as in-between magnet face & coil?
If so I plan to keep it less than .010"
The coils are .25" at their closest point.
& as for teeth? as in teeth cut out of a larger iron plate like the original axial flux motors from way back?
From my observations the most effecient motor examples are not running with a machined stator & lap wound teeth. As I am understanding, that is where the compounding iron losses come from. Although the size isn't altogether daunting. I am not certain I am willing to get to that complexity starting out.The Cisro is a corless lapwound wonder of litz wire, Halbauch & prolly a sold soul or two
If we get 90%+ out of the gate I will be stunned. But I think refining once we have some compairable set ups are going to teach us a lot.
JohninCR, The intended method of the stator production will essntialy be a casting with the coils encapsulated in the unit. Here is a good example of the proccess, scroll down to the stator casting section- http://www.otherpower.com/stator.shtml
I will be using more advanced materials. There are many options for the filler/structural ellemnts & I have a few methods that will alow active air cooling flow through the stator itself. I haven't ruled out any material as of yet with the exception of conductables (graphites & carbon fiber are connductive) I have a LOT of composite construction experiance. Right now I am leaning toward a honeycomb structure machined to the corect thickness for laminating the stator unit. Once asembled it is unbelivably strong & light weight. Thermal ranges of materials are taken into consideration also.
I am playing with a design that will alow me to make the coils removable from the main bearing hub, but the 18 tooth stator doesn't meet the critera for that option. Prolly 12 teeth would be the limit for a re-configurable stator.
Edit: fixed some spelling-----
If so I plan to keep it less than .010"
The coils are .25" at their closest point.
& as for teeth? as in teeth cut out of a larger iron plate like the original axial flux motors from way back?
From my observations the most effecient motor examples are not running with a machined stator & lap wound teeth. As I am understanding, that is where the compounding iron losses come from. Although the size isn't altogether daunting. I am not certain I am willing to get to that complexity starting out.The Cisro is a corless lapwound wonder of litz wire, Halbauch & prolly a sold soul or two
If we get 90%+ out of the gate I will be stunned. But I think refining once we have some compairable set ups are going to teach us a lot.
JohninCR, The intended method of the stator production will essntialy be a casting with the coils encapsulated in the unit. Here is a good example of the proccess, scroll down to the stator casting section- http://www.otherpower.com/stator.shtml
I will be using more advanced materials. There are many options for the filler/structural ellemnts & I have a few methods that will alow active air cooling flow through the stator itself. I haven't ruled out any material as of yet with the exception of conductables (graphites & carbon fiber are connductive) I have a LOT of composite construction experiance. Right now I am leaning toward a honeycomb structure machined to the corect thickness for laminating the stator unit. Once asembled it is unbelivably strong & light weight. Thermal ranges of materials are taken into consideration also.
I am playing with a design that will alow me to make the coils removable from the main bearing hub, but the 18 tooth stator doesn't meet the critera for that option. Prolly 12 teeth would be the limit for a re-configurable stator.
Edit: fixed some spelling-----
For a coreless motor, it's important that the stator be extremely thin to keep the gap short. This tends to make cooling difficult and the stator has to handle the full torque of the motor without deforming. I think a cored design will be more robust for a EV application. Most industrial motors use the core steel as the supporting member for the coils, which will be subjected to high forces. If using a composite, it must be very strong. You can use metal inside and outside the ring of the magnets. An aluminum ring that makes contact with the outside edge of the copper windings can be used to carry away heat.
The Mars brushless motor uses a spiral wound core something like TD showed earlier, but it is all one piece and connected behind the teeth. This is a single axial gap design.
Putting magnet rotors on both sides of the stator (dual gap design) seems like it should improve the power density but it may not necessarily be that much better than a single gap. The efficiency could be nearly as good with a single gap, it will just need to be larger to get the same power.
Assuming you can embed the cores and windings in some kind of composite matrix that is strong enough, then the real challenge is just making the cores. Keep in mind that the cores should not be covered with the composite and should stick though in order to keep the gap short. My experience is that the optimum gap will be 1-2mm. Anyway, you just make it about at close as you can get it without touching.
One way to make toothless cores would be to take a strip of iron and keep folding it over to make a sort of oval spiral. You'd probably have to try a few to get the size right. If you start with a straight section and fold it sharply, it should build up into an oval shape.
I'm not exactly sure what they use for insulation between laminations. I know it's super thin and it doesn't seem to matter much if they have a little continuity. I think it's some kind of varnish that's just painted on.
Here's an industrial strength datasheet on motor lamination steel: http://www.ussteel.com/corp/sheet/cr/cold-rolled-motor-lamination.asp
I've always thought the powdered iron core idea was good, but you don't see it used much for some reason. I think the problem is it fractures too easily. If the cores were part of a composite structure, then perhaps there wouldn't be so much stress on them and powdered iron cores might work OK. Here's somebody that did it: http://scolton.blogspot.com/2009/09/whats-next-epic-axial-motor.html
Whether or not to put teeth on the cores is another question. Normally there are teeth to fill in most of the space between the windings. You get a better flux distribution with teeth, but at high loads they tend to saturate anyway, so don't help much there. At lower loads, they help reduce the torque ripple, which improves efficiency.
The Mars brushless motor uses a spiral wound core something like TD showed earlier, but it is all one piece and connected behind the teeth. This is a single axial gap design.
Putting magnet rotors on both sides of the stator (dual gap design) seems like it should improve the power density but it may not necessarily be that much better than a single gap. The efficiency could be nearly as good with a single gap, it will just need to be larger to get the same power.
Assuming you can embed the cores and windings in some kind of composite matrix that is strong enough, then the real challenge is just making the cores. Keep in mind that the cores should not be covered with the composite and should stick though in order to keep the gap short. My experience is that the optimum gap will be 1-2mm. Anyway, you just make it about at close as you can get it without touching.
One way to make toothless cores would be to take a strip of iron and keep folding it over to make a sort of oval spiral. You'd probably have to try a few to get the size right. If you start with a straight section and fold it sharply, it should build up into an oval shape.
I'm not exactly sure what they use for insulation between laminations. I know it's super thin and it doesn't seem to matter much if they have a little continuity. I think it's some kind of varnish that's just painted on.
Here's an industrial strength datasheet on motor lamination steel: http://www.ussteel.com/corp/sheet/cr/cold-rolled-motor-lamination.asp
I've always thought the powdered iron core idea was good, but you don't see it used much for some reason. I think the problem is it fractures too easily. If the cores were part of a composite structure, then perhaps there wouldn't be so much stress on them and powdered iron cores might work OK. Here's somebody that did it: http://scolton.blogspot.com/2009/09/whats-next-epic-axial-motor.html
Whether or not to put teeth on the cores is another question. Normally there are teeth to fill in most of the space between the windings. You get a better flux distribution with teeth, but at high loads they tend to saturate anyway, so don't help much there. At lower loads, they help reduce the torque ripple, which improves efficiency.
Even the state of the art in SMC material has lower permeability than steel, so less torque. I'm not sure how the losses compare... Apparently, the trick is to use a motor design that takes advantage of the 3D flux properties of SMC.rhitee05 said:
My vote goes to a laminated steel core.
Thud
1 MW
Fetcher,
Thanks for the input, The linc to USS was a very clear explanation of eddie curent & effects.
I would really value your opinion as it sounds you have experiance in this feild.
Q-do you have any off the cuff assumptions regarding the goal of this project.
"To build a motor that rivals the performance of the budget priced outrunners, with a reasnable Kv. more easliy addapted to bicycles"
consider the 2nd larger motor an aside. The original plan was a 5-6" max diameter.
please be frank. I have thick skin & it is my thread after all
I really have no concerns regarding the building of the current models we have dipicted in this tread & holding the tollerances. That will be the easy part for me. Performace of said motor is where it gets cloudy. Given I have studyied electricity as employed in motors for about 4 weeks now, in my spare time, I am easily rattled when some new information is injected. Low confidence in that area.
I may look into haveing some flux rings laser cut.(I have a friend I can tap for that, if he can fit it into his schedual) That would be a time saver. Magnets should be in hand this week. I think I have all the composit stuff needed in the drop box. The budget is tight & Chrismas shoping has begun.(no more budget for a month or 2 :lol: ) I am anxious to get making some chips.
This forum has been awsome in gathering information presenting it. Everyone has been understanding/pateint & very helpfull. I find it humbling that anytime anyone shows a lack of understanding on some piont, The information is thoughtfully re-presented to attemt to educate. This really is a unique gaterering of exceptional humans.
Lets keep it rolling. Todd
Thanks for the input, The linc to USS was a very clear explanation of eddie curent & effects.
I would really value your opinion as it sounds you have experiance in this feild.
Q-do you have any off the cuff assumptions regarding the goal of this project.
"To build a motor that rivals the performance of the budget priced outrunners, with a reasnable Kv. more easliy addapted to bicycles"
consider the 2nd larger motor an aside. The original plan was a 5-6" max diameter.
please be frank. I have thick skin & it is my thread after all
I really have no concerns regarding the building of the current models we have dipicted in this tread & holding the tollerances. That will be the easy part for me. Performace of said motor is where it gets cloudy. Given I have studyied electricity as employed in motors for about 4 weeks now, in my spare time, I am easily rattled when some new information is injected. Low confidence in that area.
I may look into haveing some flux rings laser cut.(I have a friend I can tap for that, if he can fit it into his schedual) That would be a time saver. Magnets should be in hand this week. I think I have all the composit stuff needed in the drop box. The budget is tight & Chrismas shoping has begun.(no more budget for a month or 2 :lol: ) I am anxious to get making some chips.
This forum has been awsome in gathering information presenting it. Everyone has been understanding/pateint & very helpfull. I find it humbling that anytime anyone shows a lack of understanding on some piont, The information is thoughtfully re-presented to attemt to educate. This really is a unique gaterering of exceptional humans.
Lets keep it rolling. Todd
John in CR
100 TW
Todd,
Please share your stator cooling ideas. Have you found a strong resin that also has a high coefficient of thermal conductivity and high temp limits. With these guys wanting to use kapton tape instead of magnet wire varnish, we're talking about hot. I'm thinking that a castable ceramic may be the way to go to get the strength and thermal conductivity we want. http://www.cotronics.com/vo/cotr/pdf/onepg700.pdf . Though the magnetic and electrical properties are unclear for the #770 ceramic that has the best thermal conductivity. Even 30 btu in/hr°F ft2 may be too low, but at least we won't have to worry about a resin meltdown.
John
Please share your stator cooling ideas. Have you found a strong resin that also has a high coefficient of thermal conductivity and high temp limits. With these guys wanting to use kapton tape instead of magnet wire varnish, we're talking about hot. I'm thinking that a castable ceramic may be the way to go to get the strength and thermal conductivity we want. http://www.cotronics.com/vo/cotr/pdf/onepg700.pdf . Though the magnetic and electrical properties are unclear for the #770 ceramic that has the best thermal conductivity. Even 30 btu in/hr°F ft2 may be too low, but at least we won't have to worry about a resin meltdown.
John
Thud
1 MW
John,
Excelent points to consider. I know we will be creating heat. & a lot of guys are not afraid to create a LOT of heat also. The resins are going to be the weak link in the stator. Something in the polyester familys look better than the epoxy's that are on the shelf but even those are in trouble long before any of the electric systems are. By creating the stator core matrix in 1/2's or more sections, we can cut any number of patterns & ducts throught the stator. Higher temp rated phenolics my be employed but I really will have a hard time justifying building an oven to cure something like that to my better half.
I have considered making coil surounding shells of heavily groged mullite that would ajoin the air ducts to transfer heat out of the stator right where it is created. I may also experiment with resin bonded perlite, for ease of production.(wouldn't have to fire up the kiln) I have made a few crucibles to service my metal casting interests, so ceramics are definatly in the mix. I think thermal insulation to keep the heat some where where we can attempt to controll it will be paramount to the folks who will undoubtably abuse our industrial art.
Here is a home made crucible:
The one on the right is unfired.
The clam shell rotor set up we are trying, lends itself perfectly to adding vains in that space & creating positive airflow. openings in the stator will allow cooling air to flow directly up & around the coils. again its easyer to model than explain, and the 18 coil stator is very crowded.
Axel has employed water cooling on a number of his builds. I think air is a better option as it works well with electricity & it is already there anyway. We just need to push it around a little.
Excelent points to consider. I know we will be creating heat. & a lot of guys are not afraid to create a LOT of heat also. The resins are going to be the weak link in the stator. Something in the polyester familys look better than the epoxy's that are on the shelf but even those are in trouble long before any of the electric systems are. By creating the stator core matrix in 1/2's or more sections, we can cut any number of patterns & ducts throught the stator. Higher temp rated phenolics my be employed but I really will have a hard time justifying building an oven to cure something like that to my better half.
I have considered making coil surounding shells of heavily groged mullite that would ajoin the air ducts to transfer heat out of the stator right where it is created. I may also experiment with resin bonded perlite, for ease of production.(wouldn't have to fire up the kiln) I have made a few crucibles to service my metal casting interests, so ceramics are definatly in the mix. I think thermal insulation to keep the heat some where where we can attempt to controll it will be paramount to the folks who will undoubtably abuse our industrial art.
Here is a home made crucible:
The one on the right is unfired.
The clam shell rotor set up we are trying, lends itself perfectly to adding vains in that space & creating positive airflow. openings in the stator will allow cooling air to flow directly up & around the coils. again its easyer to model than explain, and the 18 coil stator is very crowded.
Axel has employed water cooling on a number of his builds. I think air is a better option as it works well with electricity & it is already there anyway. We just need to push it around a little.
Thud said:Q-do you have any off the cuff assumptions regarding the goal of this project.
"To build a motor that rivals the performance of the budget priced outrunners, with a reasnable Kv. more easliy addapted to bicycles"
consider the 2nd larger motor an aside. The original plan was a 5-6" max diameter.
please be frank. I have thick skin & it is my thread after all
I think it can be done. There is not much on the market in that size range, and most of those are super expensive. It would be good to pay attention to how they build the larger RC motors, as they seem to have very good efficiencies and power densities. The key items are good magnets, good iron, and close tolerances.
If you can get the efficiency high, it will reduce the heating tremendously. Going from 80% to 90% efficiency cuts the heat dissipation in half. I'd try and do direct conduction to the coils if possible, so the motor could be sealed. If that gets too hot, then go for forced-air cooling. The copper in the windings is an excellent heat conductor, so if one side of the coil is pressed against a big heat sink, the entire coil will be cooled. Metal-filled epoxy isn't too bad for heat conduction, but is limited in max. temperature. Silicone rubber is amazingly good at conducting heat and can survive 500F, but it is not very strong. Ceramic is an interesting thought, but would be difficult to make and somewhat brittle. It may be useful as a filler between the coils to help carry away heat.
Thud
1 MW
Fetcher,
Thank you.
I really hadn't considered silicone as a heat transfer medium. But I love working with the stuff. I am opening the imagination another notch (like my belt on thanksgiving day)that is another option in the matrix that will be the stator.
Thank you.
I really hadn't considered silicone as a heat transfer medium. But I love working with the stuff. I am opening the imagination another notch (like my belt on thanksgiving day)that is another option in the matrix that will be the stator.
Thud
1 MW
Miles,
I think if not cost prohibitve, that would be a solution. Asuming the performance is not degraded by thinning for the lamination of the final skin of the stator. As a internal bonding agent potting resin may fit the bill.
I think if not cost prohibitve, that would be a solution. Asuming the performance is not degraded by thinning for the lamination of the final skin of the stator. As a internal bonding agent potting resin may fit the bill.
John in CR
100 TW
If you want to stick with resins, it's vinyl ester resin that offers higher temp handling than the epoxy resins, and at the same time it rivals epoxy in strength. It's also about half the price of epoxy. The downfall is that it's nasty stuff to work with and off gases bad fumes. I had a motor rewound and that's what the shop slathered on the windings to hold them in place. We want to avoid extreme temps anyway, because it will cook our neo magnets, so the kapton tape is probably not needed unless we also invest the extra $ in high temp magnets.
There's plenty of high quality brainpower around here, so let's come up with a 95% efficient motor with a broad high efficiency band making the easy passive ventilation of an axial motor sufficient to keep it nice and cool.
John
There's plenty of high quality brainpower around here, so let's come up with a 95% efficient motor with a broad high efficiency band making the easy passive ventilation of an axial motor sufficient to keep it nice and cool.
John
rhitee05
10 kW
High-temp materials with good thermal conductivity definitely seem like a good idea. Maybe not for the prototype, but I wouldn't discard the idea of water cooling. If you want something with the kind of power density LFP is craving, you're going to be hard-pressed to get enough airflow to keep it from melting. If you can get a wrap or two of copper pipe in good thermal contact with the windings, it would go a long way toward solving heat problems! Maybe one wrap around the inside and one around the outside, away from the flux path to avoid eddy currents.
If you really want to melt your brain, read this:
http://www.ornl.gov/~webworks/cppr/y2001/rpt/120491.pdf
While their example is a radial motor, all the same principles apply. And the math.
Can you imagine? People actually getting paid to work on stuff like this... I do it for free.
http://www.ornl.gov/~webworks/cppr/y2001/rpt/120491.pdf
While their example is a radial motor, all the same principles apply. And the math.
Can you imagine? People actually getting paid to work on stuff like this... I do it for free.
Thud
1 MW
Fetcher,
Thanks, that was a good read.I will be printing this & using it as bed side material as there is too much to absorb in a quick read-over.
For anyone not interested in reading the whole thing, brows to the bottom of page 80 & go thru a page or 2. it is all relaveant to our current point of discusion in this thread. & It confirms my gut feeling, when looking at different motor topologies side by side.
Thanks, that was a good read.I will be printing this & using it as bed side material as there is too much to absorb in a quick read-over.
For anyone not interested in reading the whole thing, brows to the bottom of page 80 & go thru a page or 2. it is all relaveant to our current point of discusion in this thread. & It confirms my gut feeling, when looking at different motor topologies side by side.
Thud
1 MW
This morning I made time to model the active cooling idea, here are some visuals to illistraight the method.
Don't get stuck on the halves represented as monolithic slabs. Or the pole count, its just easyer to draw that way.
Also I havn't given any time yet to the vain structure of the venting rotor. This drawing may be a high pitch siren atm but we will addres that later. It will be a cast plastic item when the time comes.
Here it is in position about the stator-no coils or magnet rotors in the view.
now you see the exit holes in the stator edge:
you can see also the mounting ring to attach it to the main bearing hub.
another look with the stator seperated on center:
and here in close up, foward 1/2 rotated 180:
Again, I think the entire area about the coils can be sub structure from any number of temprature apropriate materials. The key will be keeping the heat generated low with efficent winds & controlling its path out of areas that will affect mechanical support of the stator itself.
Don't get stuck on the halves represented as monolithic slabs. Or the pole count, its just easyer to draw that way.
Also I havn't given any time yet to the vain structure of the venting rotor. This drawing may be a high pitch siren atm but we will addres that later. It will be a cast plastic item when the time comes.
Here it is in position about the stator-no coils or magnet rotors in the view.
now you see the exit holes in the stator edge:
you can see also the mounting ring to attach it to the main bearing hub.
another look with the stator seperated on center:
and here in close up, foward 1/2 rotated 180:
Again, I think the entire area about the coils can be sub structure from any number of temprature apropriate materials. The key will be keeping the heat generated low with efficent winds & controlling its path out of areas that will affect mechanical support of the stator itself.
The flat wire is cool, but I bet it's expensive.
Thud, I'm not sure I follow what you're doing with the cooling passages. If you want air to circulate around the windings like that, you'd need a much larger passage to be effective. Water cooling, on the other hand, would probably be very effective with an arrangement like that.
I think it may be good enough if the outside edge of the coil pushes against an aluminum ring on the outside of the stator. If the outer housing was also aluminum and bolted to this ring, it would have a lot of cooling capacity.
Another approach might be to have some kind of fins on the rotor(s) that will circulate air from near the shaft to the outer edge of the rotor like a vacuum cleaner. This will draw air across the face of the coils where you have a lot of surface area. This would reqire rather large holes or spokes in the rotor and stator between the shaft and the ring of the magnets and vents in the outer housing like you show.
Thud, I'm not sure I follow what you're doing with the cooling passages. If you want air to circulate around the windings like that, you'd need a much larger passage to be effective. Water cooling, on the other hand, would probably be very effective with an arrangement like that.
I think it may be good enough if the outside edge of the coil pushes against an aluminum ring on the outside of the stator. If the outer housing was also aluminum and bolted to this ring, it would have a lot of cooling capacity.
Another approach might be to have some kind of fins on the rotor(s) that will circulate air from near the shaft to the outer edge of the rotor like a vacuum cleaner. This will draw air across the face of the coils where you have a lot of surface area. This would reqire rather large holes or spokes in the rotor and stator between the shaft and the ring of the magnets and vents in the outer housing like you show.
Thud
1 MW
Fechter,
claification- The green dipiction is a fan rotor the nestles between the magnet rotors.(roughly modeled) It spins with the rotors.The vains will create positive airflow through the stator wich is stationary, none of the pasage sizes have been optimized. Just a visual aid to show the concept of active air cooling.
In a perfect world we wouldn't need it. History of this design shows otheres have had issues regading cooling.
claification- The green dipiction is a fan rotor the nestles between the magnet rotors.(roughly modeled) It spins with the rotors.The vains will create positive airflow through the stator wich is stationary, none of the pasage sizes have been optimized. Just a visual aid to show the concept of active air cooling.
In a perfect world we wouldn't need it. History of this design shows otheres have had issues regading cooling.
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